The maximum installed capacity mathematic model has been set up and analysis about surface water source heat pump using at large scale. The maximum installed capacity of Nu River China has been calculated by the equations as an example. In the mean time, the key coefficients have been simplified while practical application in engineering. A general conclusion of the maximum water source heat pump installed capacity has obtained for different surface water characteristic. The value from the general conclusion can use in the plan and the layout on the surface water source heat pump system large-scale use. That will protect ecological environment and against creates the destruction.